The MPEG-2 video compression standard has been successfully adopted in digital TV broadcasting. As with many other popular image and video compression standards, MPEG-2 uses block-based Discrete Cosine Transforms (DCT). The basic approach of this DCT-based image and video compression technique is to subdivide the image into 8×8 blocks of pixels and then individually transform, quantize, and encode each block.
However, this block-based coding technique introduces blocking artifacts between block boundaries because the transform does not take into account the correlation between block boundaries. As high picture quality display technologies emerge rapidly, and TV screens get ever larger, the blocking artifacts are more visible and more annoying.
In order to improve the quality of the received images for display, it is necessary to provide the receiver end with a post-processor to remove blocking artifacts in the decoded video streams. The basic requirements for such types of de-blocking post-processors are removing blocking artifacts, preserving image edges, and being cost-effective (i.e., low-complexity and low-memory requirement).
Many post-processing techniques have been developed for reducing blocking artifacts, such as image adaptive filtering (T. Liu, et al., “Adaptive Post-processing Algorithms for Low Bit Video Signals,” IEEE Tans. on Image Processing, vol. 4, July 1995); projection on convex sets (Y. Yang, et al., “Projection-based Spatially Adaptive Reconstruction of Block-transform Compressed Images,” IEEE Trans. on Image Processing, vol. 4, July 1995); wavelet de-noising (R. Gopinath, et al., “Wavelet-based Post-processing of Low Bit Rate Transform Coded Images,” ICIP 1994); and non-linear diffusion (S. Yang, et al., “Coding Artifacts Removal Using Biased Anisotropic Diffusion,” ICIP 1997).
Although such conventional techniques have led to improved image quality, most require either a large amount of computation time or a large amount of memory, and as such, are not suitable for real-time video applications. There is, therefore, a need for a post-processing method and apparatus that are simple and require low-memory, and which can efficiently remove blocking artifacts without blurring image edges. There is also a need for such method and apparatus to have a simple architecture be easy for hardware implementation.